You can read about the fixes included in the April CU from the following articles:

Server Rollup Packages:

(http://support.microsoft.com/kb/981043/ ) Description of the Windows SharePoint Services 3.0 Cumulative Update Server Hotfix Package (WSS server-package): April 27, 2010

http://support.microsoft.com/kb/981043/

Description of the Office SharePoint Server 2007 Cumulative Update server hotfix package (MOSS server-package): April 27, 2010

http://support.microsoft.com/kb/981042/

Individual Product Packages:

Description of the Windows SharePoint Services 3.0 Cumulative Update server hotfix package (Sts-x-none.msp): April 27, 2010

http://support.microsoft.com/kb/981040/

Description of the Project Server 2007 hotfix package (Pjsrvapp-x-none.msp; Pjsrvwfe-x-none.msp): April 27, 2010

http://support.microsoft.com/kb/981044

Description of the Office Project 2007 hotfix package (Project-x-one.msp): April 27, 2010

http://support.microsoft.com/kb/981732/

Client Installation:

In order to install this hotfix, you will need to have Microsoft Project 2007 SP1 installed on the client. The article at the URL below contains information on how install download and install SP1 should you not have it installed already.

Note:  We strongly recommend that you install Project 2007 SP2 from the information earlier in the article.

Description of Project 2007 Service Pack 1 and of Project Language Pack 2007 Service Pack 1

http://support.microsoft.com/kb/937154/en-us